The present invention relates to a telephoto zoom lens system in a zoom lens for use in 35 mm photographic cameras, the lens system having a zoom ratio of about 3 for covering semi-telephoto and telephoto ranges.
Many telephoto zoom lenses of the type described are known which have a zoom ratio of about 2.5. A telephoto zoom lens according to the present invention has a telephoto ratio (the ratio of the distance between the front lens and the image plane to the focal length at a maximum focal length) of 0.94 for compactness and an increased zoom ratio of about 3, while achieving high performance. A telephoto lens having a zoom ratio of about 2.5 is disclosed in U.S. Ser. No. 240,421, now U.S. Pat. No. 4,395,092, filed by the present applicant. The zoom ratio of disclosed zoom lens is smaller than that of the lens system of the present invention, and the number of lenses is 12 divided into 9 groups while the relay lens system includes a rear group (referred to as "fourth lens group b") composed simply of two-group two-lens elements, with the result that the lens system is of high performance. Japanese Patent Publication Laid-Open No. 56-42208 discloses a telephoto zoom lens having a zoom ratio of about 3. This telephoto zoom lens is composed of nine-group twelve-lens elements or ten-group thirteen-lens elements with the fourth lens group b composed of two-group two-lens elements. However, the telephoto zoom lens fails to achieve high performance since the curvature of field varies widely as the focal length changes. An attempt to make the lens compact in size and correct the curvature of field while maintaining the fourth lens group b of the two-group two-lens type would result in a reduction of the brightness of the marginal portion of the image field or in an increase of coma aberration and distortion.